Global Schr\"odinger map flows to K\"ahler manifolds with small data in critical Sobolev spaces: High dimensions

Abstract

In this paper, we prove that the Schr\"odinger map flows from $\Bbb R^d$ with $d\ge 3$ to compact K\"ahler manifolds with small initial data in critical Sobolev spaces are global. This is a companion work of our previous paper [23] where the energy critical case $d=2$ was solved. In the first part of this paper, for heat flows from $\Bbb R^d$ ($d\ge 3$) to Riemannian manifolds with small data in critical Sobolev spaces, we prove the decay estimates of moving frame dependent quantities in the caloric gauge setting, which is of independent interest and may be applied to other problems. In the second part, with a key bootstrap-iteration scheme in our previous work [23], we apply these decay estimates to the study of Schr\"odinger map flows by choosing caloric gauge. This work with our previous work solves the open problem raised by Tataru.